The ability to produce high quality microelectronic devices and reduce yield losses is strongly dependent upon maintaining the surfaces substantially defect-free. This is particularly true as design rules drive integrated circuits to finer feature size. Generally, surface defects can be related to particulate matter being deposited onto surfaces of reticles (masks) and wafer substrates during the various operations required to produce integrated circuits. The need to maintain these surfaces substantially free of particulate matter has long been recognized in the microelectronics industry and various schemes to do so have been proposed, such as those set forth in U.S. Pat. Nos. 5,373,806 and 5,472,550. The former discloses the use of thermal energy, such as the use of radiant energy, RF, or resistance heating, to substantially eliminate electrostatic attraction as a mechanism for particle transport and deposition during gas phase processing while the latter describes the use of the photophoretic effect to capture particles by projecting a laser beam inside the processing chamber along a trajectory that does not contact the substrate surface.
The concern about printable defects caused by particle deposition onto surfaces is of particular importance for the next generation of lithographies, including proximity x-ray lithography, direct-write and projection electron-beam lithography (SCALPEL), direct-write and projection ion-beam lithography, and extreme ultraviolet (radiation having a wavelength in the region of 3.5-15 nm) lithography (EUVL) which must provide for exclusion of particles with diameters greater than 0.01 μm.
Because of the importance of protecting lithographic surfaces, such as reticles, from deposition of particulate matter for next generation lithographies alternative protection schemes such as clean encapsulation of the exposure chamber, protective gas blankets, and in situ cleaning of mask surfaces are being investigated. However, each of these alternative schemes has disadvantages and none has been developed to the point of application.
What is needed is a means to protect lithographic surfaces, such as those of the reticle and wafer, from particle deposition without comprising lithographic performance or contaminating lithographic optical elements. Moreover, in order to be useful in advanced lithographic applications it is necessary that the protecting means operate effectively in a sub-atmospheric pressure environment.